Overload apparatus



Feb. 8, 1944. c. A. Rn-fTz ETAL Q 9 7 A OVERLOAD APPARATUS Filed Aug. 2, 1940 F'IE L W '64 INVENTORS M 59/4 4. E/e/j 1- Q I BY ,d/VE/O f.

ATTORNEY Patented Feb. 8, 1944 ovnnLoAn APPARATUS Carl A. Rietz and Alvero E. Smith, San Francisco, Calif.

, Application August 2, 1940, Serial No. 349,662

' roam. (o1. 200-112) This invention relates generally to devices for the protection of electric. motors, particularly in order to safeguard against overloads.

In the installation of various electric motors.

such as motors used in various processing plants, it is customary to employ a starter having some protection against heavy overloads. Such protection, however, is arranged with a time delay before release of the starter, and is not capable of accurate adjustment to suit varying conditions and requirements.

It is an object of the present invention to provide apparatus which will afford instantaneous overload cutout for electric motors, and which can also be readily adjusted so that the extent of overload before cutout can be adjusted to suit requirements. 1

A further objectof the invention is to provide an overload relay having means for varying both the point of cutout and pickup with respect to the current flow to the motor and also means for adjusting or varying the margin between cutout and pickup. I

Additional objects of the invention will appear from the following description in which the preferred embodiment is described in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Figure 1 is a plan view of an overload relay incorporating the present invention, and also showing certain connections between the relay and an electric motor together with its starter;

Figure 2 is a cross sectional view taken alongthe line 22 of Figure 1; and I Figure 3 is a wiring diagram.

Referring first to Figure 1 of the drawing, the apparatus includes an electric motor I which in this instance is operated on three phase alternating current. The conductors Tl, T2 and T3 connected to this motor extend from terminals of a starter box Current supply lines Ll, L2 and L3 also connect with the starter box. It is presumed that the starter in this instance is provided with a magnetic coil, which when energized or de-energized will result in instantaneous tripping of the starter to interrupt current supplied to the motor.

The overload relay I2 is used in conjunction with the above mentioned trip coil of the starter. This relay includes the electromagnet |3 which has a winding l4 and spaced magnetic pole pieces I4. The entire electromagn'et together with other parts of the relay are secured to a suitable mounting plate or panel 16. In order to make possible a certain type of adjustment, the magnetic core for winding l4 includes one section II, and another section l8 which is in the form of a threaded plug and which can be turned to advance or retract it with respect to the core section l1. By this arrangement the air gap l9 between the sections l1 and |8 can be adjusted, to thereby adjust the strength of the magnetic field between the pole pieces 20.

Mounted between the pole pieces 2|) there is a magnetic armature 2|, which has a pivotal connection 22 to the fixed supporting plate Hi. This armature may oscillate between two limit ing positions, one of which is adjustable. One limiting position is established by the shoulder 24 on one of the pole pieces 20, and the other by the adjustable stop screw 26 whichis carried by the bracket 21. Normally the armature is urged against the stop screw 26 by the spring 28. Tension upon this spring can be adjusted, as by having the spring anchored to an upwardly bent arm 29, which is carried by a bracket 3|. By turning arm 29, the angle of pull of the spring 28 with respect to the armature 2| can be adjusted, thus in effect varying the bias upon th armature. 4 1

The contacting means for the relay is a switch unit 32 of the Mercoid type, which is adapted to be tilted between off and on positions. The flexible leads 33 from unit 32 connect to the terminals 34 and 36. This unit or cartridge is removably clipped within a mounting 31, which in turn has a pivotal connection 38 to the supporting plate 39. For reasons to be presently explained, plate 39 is secured to panel IS in such a manner as to permit lateral adjustments, as for example by providing the slot 4| to accommodate the attachment screws 42.

In order to operably connect the mounting 31 to armature 2|, the mounting is provided with an arm 43, the free end of which carries a pin 44. Pin 44 engages one side of an arm 45 extending at right angles to the armature 2|. Mounting 31 is also biased in a counterclockwise direction as viewed in Figure l, by means of the attaching spring 46. Tension upon this spring can be adjusted by changing the setting of the anchoring screw 41. It will be evident that turning of armature 2| in a counterclockwise direction as viewed in Figure 1 causes switch unit 32 to turn in a clockwise direction, and that as the armature turns toward its limiting position, the Mercoid switch unit will reach a position in which its inner contacts will be opened or closed, as the case may be. Preferably such operation of the Mercoid switch unit takes place for movement of the armature from its limiting position shown in Figure 1, to another position short of engagement with the stop 24.

Connection of the relay described above with the motor l0 and the starter H is as follows: The terminals 49 of winding l4 are connected in series with one of the current supply conductors leading to the motor In. In this connection it should be noted that the resistance or impedance ofthe winding l4 should be relatively tion between conductor 55 and terminal 530i the starter box. Movable contacts Elwhen.

closed serve to short out the lVlercoid'swi-tchi Assuming now that the relay is adjusted units.

for cutout at 100% overload, the motor will ,function normally for all ordinary loads, and because of current flow through winding H5, magnetic flux will act upon armature iii to hold this-,a1- mature in an intermediate position away from the backstop screw 26. If a 100% overload ocev curs upon the motor I!) current fiow to the motor is increased to a value sufficient to cause the .armature 2! to turn to a position to operate the Mercoid switch unit 32. Thus the contacts of this switch unit are opened, and as a result the trip coil within the starter ii isoperated immediately to release the. starter and thus interrupt supply of current to the motor. After the load upon the motor. It has beenremoved, one may again start the motor by operating contacts 52 of the manual switch Fail, together with manual operation of the starter ii, if the starter is of such a character that such manual operation is required.

The overload relay described above has certain desirable characteristics. By changing the setting of the core section Is, it is possible to. adjust the percentage overload at which the relay will cut out and interrupt supply of current to the motor. Such adjustment will maintain the same general margin between cutout and pickup. In other words, if the relay is arranged to cut out at 100% overload, and to again close the Mercoid switch unit at 8.0% overload,,the. margin between 80 and 100% will be retained after adjustment ,of the core section is, although after such adjustment the relay may cut out'at say 150% overload, and pick up at say 130% overload. It is also possible to adjust the margin between cutout and pickup conditions. This is accomplished by adjusting the position of the. mounting plate 30, for the Mercoid switch unit. Ashifting of this plate from one position to another has the efiect of changing the angle of switch unit 32 for a given positionof the, armature 2!. Therefore, the relay can be made quite sensitive so that a relatively small amount .of movement of the armature 21 away from the ad justable stop 26, will serve to shift the Mercoid switch unit between closed and opened positions. Additional adjustment can be made by changing the stop screw 26, and by changing the bias afforded by spring 28. A change in the bias of spring 28 makes possible relatively-fine adjustment, thus making it possible to adapt the relay to particular requirenwntsv after a general setting has been made by turning the core section 18.

Figure 3 illustrates a system making use of two motors, where a condition of overload upon one motor acts through the overload relay for starting and stopping the second motor. Thus in this case one motor Bl operates a disintegrator 62, as for example a machine of the type disclosed in my Patent No.- 2,153,590. Another Inctor 63 drives a feeder 64, as for example a feeder of the sc ew ype, which su es er alwto the disintegrator 62. The starter 61 connects between the current supply line and the motors 6| and 63. The terminal 49 of winding 14 are connected in series with one conductor leading to motor Bl. One terminal 34 of the Mercoid switch unit 32 is connected by a conductor 68 to the terminal 69 of starter G1. The other terminal 36 of Mercoid switch unit 32 connects through the manual switches H and 12 to the terminals 52 and 53 of starter 66, as illustrated. Switch 12 is usually located at a remote point, closing of contact 14 being for starting of motor BI, and opening of contact 13 being for stopping. Closing of switch arm 16 of switch H places motor 63"under the automatic control of the relay l2, while closing of arm l1 shuts out the Mercoidswitch unit-.32, and places motor 63 under the full manual control of the switch 72.

Toexplain operation. of the system illustrated in' Figure 3, it will be presumed that the relay I2 is :setto operate when a overload is placed upon the motor 6|. At the same time it will .be presumed that feeder 64 normally supplies an :amount of material to the disintegrator 62,. such as will maintain a torque upon the motor Bl corresponding to the full rated capacity of the motor. A greater load upon the motor BI will be because of a greater amount of materialbeingfed to the disintegrator by the feeder 64. If thedisintegrator is supplied with material such that a.20% overload is placed upon motor 6|, relay I2 is set to tripMercoid switch 32 to immediately cause interruption of current supply tothe motor 63. When the disintegrator clears itself and the load returns to normal, the currentflow to the motor Si is again reduced so that the relay [2 operates through starter 61 to re-establish current supply to motor 63. In this connectionit'will be noted that the conductor 6.8. connects to a .Coil associated with starter 61, so that when this coil is energized by current flow throughv switch 32, the main current flow to motor 63 is interrupted. When switch 32 is. opencircuited, starter 6,! automatically reestablishes. current supply to the motor.

For the automatic operation described above, armlfi of switch II should .be closed, and arm 11 opened. ,Where hand operation is desired from a position adjacenttherelay, switch arm ll is closed to shut out .the Mercoid switch unit ,32. Manual switch." can .be located .at a remote point, and serves to effect manual control of motor 6 Iz, throughstarter :66.

We claim:

In an overload relay, anelectromagnet having a winding andalso having spaced magnetic pole pieces the windingrbeing adapted for connection inseries with a current carrying circuit, a pivotally mounted armature associated with the pole -pieces,-means for biasing the armature to ward one of two'limiting positions, a switch-unit of the Mercoid type, a rocker mounting for the switch unit pivotally secured to a fixed support, wherebythe switch unit is free to tilt between on and. ofipositions, means for urging the rocker mou ting in one direction and a pair of engaged lever arms secured to the armature and to the rocker mounting respectively for causing rockingof the .mounting when the armature i rotated, and ,meansfor shifting the pivotal axis of the rocker mounting relative to the pivotal axis of the armature.

' ,CARL A. RIETZ.

ALVERO E. SMITH. 

